The vehicle is a friend's 91 Z28 TPI 5.7. Also, which wires are probed to get the readings? I have done this on other cars, but never on a TPI. Thanks!

 

You would probe pin "A" (negative, wire should be black) & "B" (positive, wire should be blue). Voltage with throttle closed and ignition "ON" or at idle should read less than .96 volts. The TPS on this engine is not adjustable, it is determined by the ECM.

 

So what do you do if the voltage reading is off? The car hasn't been right at low engine speeds since the TB was installed (I haven't seen or driven it yet, just going on what the guy said). Its a Holley TB if that matters. The mechanic who installed it said he couldn't get the proper adjustment (not slotted like some of the older ones), and the owner tried to get a replacement TPS that did, or at least has some material that could be removed to make it adjustable. He got one from the dealer, and while it isn't adjustable it appears to have enough material to make it adjustable. I remember having to do this on another vehicle (can't remember what it was, possibly a Buick GN or a 5.0 Mustang), and assumed the Z28 was the same.

 

What size throttle body is it, 52MM or 58MM? The standard stock TPS for a 1991 stock 5.7L TPI engine is not adjustable, if there is a problem with the TPS. The only recourse is to replace it. The two wires to back probe are pin "A" & ""B". Pin "A" (ground) is the top wire on the TPS connector and pin "B" (positive) is the center wire. I don't know if the size of the throttle body might have an effect on it or not. It might need a TPS designed for that throttle body. BTW, what are your voltage readings?

 

Its a 52mm. I haven't looked at the car yet (the owner is bringing it over Tuesday night), so I'm not sure where the voltage is or if her even checked it. Apparently there was no problem before the new throttle body was installed, so I figured it was the TPS voltage.

 

Go to this link, maybe it will help. IAC and TPS Adjustment

 

You'll surely notice if this is the problem but myself and others have had to grind down the metal TPS tab when installing the Holley TPI throttle bodies. It rubs the housing slightly on some, and severely on others.

Also, I didn't know a '91 TPI TPS wasn't adjustable. Guess I never needed to move one of them. But, a TPS from an older model should be adjustable and work just fine. It may even be required to get it set properly.

Sounds like you know enough about it to figure all that out though.

HTH

 

Thanks a lot guys, you've all been a big help.

 

That would only apply to TPS's that are designed to be manually adjusted.